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Fe-N-C structures have been considered as a candidate to replace noble metal catalysts towards oxygen reduction reaction (ORR) due to their excellent electrocatalytic activity and durability. Herein, a zinc-mediated synthesis strategy is proposed for N-doped graphitic porous carbon encapsulated uniform dispersed Fe3C nanoparticles coupled with atomically dispersed Fe-Nx moieties (NPC/Fe-N-C) derived from biomass coconut shell. The introduction of zinc species could be conductive to the dispersion of iron species and formation of porous structures. Density functional theory calculations demonstrate that the N-doped carbon coating structures can weaken the oxygen intermediates adsorption energy barrier of Fe3C. Besides, the graphitic carbon could promote the electron transfer during the electrochemical reaction. These special structures enable NPC/Fe-N-C to have excellent ORR activity with an Eonset of 1.0 V, which is much better than Pt/C. Furthermore, the zinc-air battery assembled by pairing NPC/Fe-N-C with a high-efficiency oxygen evolution reaction (OER) catalyst can continuously and stably operate a charge-discharge potential gap of 0.8 V at 10 mA/cm2 for more than 600 hours. More importantly, the assembled batteries could drive overall water splitting device, realizing the effective energy conversion.

Journal of materials science & technology 102, 89 - 96 (2022). doi:10.1016/j.jmst.2021.06.041, In modern ��-solidified TiAl alloys, the decomposition of ��$_2$ phase is frequently observed during heat treatment or high-temperature deformation of the alloys. In this study, high-temperature deformation and decomposition mechanisms of ��$_2$ phase in a Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y alloy are investigated. In a sample deformed at 800 ��C, the precipitation of ��$_o$(��$_o$) phase is observed within the equiaxed ��$_2$ phase. The nucleation of ��$_o$ particles within the ��$_o$ matrix indicates the ��$_2$ ��� ��$_o$ ��� ��$_o$ transformation. In addition, numerous �� phase precipitates form within the ��$_o$(��) areas. The ��$_2$ lamellae decompose into ultrafine (��$_2$+��) lamellae and coarsened �� lamellae via ��$_2$ ��� ��$_2$ + �� and ��$_2$ ��� �� transformation, respectively. Moreover, the ��$_o$ phase nucleates within the ultrafine lamellae via ��$_2$ ��� ��$_o$ transformation. However, in a sample deformed at 1000 ��C, the nucleation of ��$_o$ particles is sluggish, which is caused by the efficient release of the internal stress via dynamic recrystallization (DRX). These results indicate that complex phase transformations can be introduced by the decomposition of ��$_2$ phase in TiAl alloys with a high amount of ��-stabilizing elements., Published by Ed. Board, Journal of Materials Science & Technology, Shenyang

Organic cations are essential components of locally concentrated ionic liquid electrolytes (LCILEs), but receive little attention. Herein, we demonstrate their significant influence on the electrochemical performance of lithium metal batteries via a comparison study of two LCILEs employing either 1‑butyl‑1-methylpyrrolidinium cation (Pyr14+) or 1-ethyl-3-methylimidazolium cation (Emim+). It is demonstrated that the structure of the organic cation in LCILEs has only a limited effect on the Li+- bis(fluorosulfonyl)imide anion (FSI−) coordination. Nonetheless, the coordination of FSI− with the organic cations is different. The less coordination of FSI− to Emim+ than to Pyr14+ results in the lower viscosity and faster Li+ transport in the Emim+-based electrolyte (EmiBE) than the Pyr14+-based electrolyte (PyrBE). Additionally, the chemical composition of the solid-electrolyte interphase (SEI) formed on lithium metal is affected by the organic cations. A more stable SEI growing in the presence of Emim+ leads to a higher lithium plating/stripping Coulombic efficiency (99.2%). As a result, Li/EmiBE/LiNi0.8Mn0.1Co0.1O2 cells exhibit a capacity of 185 mAh g−1 at 1C discharge (2 mA cm−2) and capacity retention of 96% after 200 cycles. Under the same conditions, PyrBE-based cells show only 34 mAh g−1 capacity with 39.6% retention.

The fabrication of solid-state single-molecule switches with high on-off conductance ratios has been proposed to advance conventional technology in areas such as molecular electronics. Herein, we employed the scanning tunneling microscope break junction (STM-BJ) technique to modulate conductance in single-molecule junctions using mechanically induced stretching. Compound 1a possesses two dihydrobenzothiophene (DHBT) anchoring groups at the opposite ends linked with rigid alkyne side arms to form a gold-molecule-gold junction, while 1b contains 4-pyridine-anchoring groups. The incorporation of ferrocene into the backbone of each compound allows rotational freedom to the cyclopentadienyl (Cp) rings to give two distinct conductance states (high and low) for each. Various control experiments and suspended junction compression/retraction measurements indicate that these high- and low-conductance plateaus are the results of conformational changes within the junctions (extended and folded states) brought about by mechanically induced stretching. A high-low switching factor of 42 was achieved for 1a, whereas an exceptional conductance ratio in excess of 2 orders of magnitude (205) was observed for 1b. To the best of our knowledge, this is the highest experimental on-off conductance switching ratio for a single-molecule junction exploiting the mechanically induced STM-BJ method. Computational studies indicated that the two disparate conductance states observed for 1a and 1b result from mechanically induced conformational changes due to an interplay between conductance and the dihedral angles associated with the electrode-molecule interfaces. Our study reveals the structure-function relationship that determines conductance in such flexible and dynamic systems and promotes the development of a single-molecule variable resistor with high on-off switching factors.

The effects of tool-workpiece relative positions on the microstructures and mechanical properties of 1-mm-thick 6061-T6 aluminum to T2 copper friction stir welds are systematically investigated in this research. Compared with the case of placing Cu sheet on advancing side, placing the Al sheet on advancing side can promote the flow of nugget material and expand the volume of the mixing zone, which is more conducive to obtain high-quality dissimilar Al-Cu welds. Based on this, the 1-mm tool offset toward Cu side is found to yield higher hardness and more defects due to the formation of Cu9Al4, leading to poor tensile properties and a brittle fracture feature of the joint. When the tool axis moves 1 mm toward the Al side, the decrease in Cu content in the stir zone not only limits the adhesion of material to the shoulder surface but also prevents the phase transformation from CuAl2 to Cu9Al4 and induces thin lamellar structures in the weld, which improves the fracture patterns and leads to good tensile properties of joint. The present study is expected to clarify the process characteristics of the dissimilar FSW of Al and Cu thin sheets and thus to promote the high-quality application of Al and Cu materials in electrical and electronic technology.

The combined use of ductile cast iron and alloy steel is beneficial, however, this technique causes some difficulties in welding due to the different properties of these two materials. In the present work, magnetically impelled arc butt (MIAB) welding a solid-state joining process, was employed to weld GGG40 ductile cast iron tube and an E355 + N alloy steel tube (each one had a thickness of 6 mm). The microstructure and mechanical properties of the resultant joints along different positions of the weld tube were systematically investigated. The heating during MIAB welding was non-uniform, causing significant changes in the microstructure, microhardness, and tensile stress of the welds. The maximum hardness of the welds (482 HV) was much higher than that of the base metal. The average (334.4 MPa) and maximum tensile strengths (382.4 MPa) of the welds were 83.6% and 95.6% of those of the base metal, respectively. These results show that MIAB is an effective method for welding ductile cast iron/alloy steel dissimilar materials.

When carbon-containing species are involved in reactions catalyzed by transition metals at high temperature, the diffusion of carbon on or in catalysts dramatically influences the catalytic perform...

Cellulose-based separators for lithium ion batteries have attracted much attention due to the good wettability and thermal stability. However, most of them are based on the expensive nanocellulose,...

The development of an efficient hydrogen spillover (HS) catalyst achieves the stoichiometric chemoselective hydrogenation of NO3− and NO2− into N2 at room temperature, which is extremely challenging. Herein, we report a CuxPd1−x nanowire network (NWN) (x = 7, 5, or 3) with tunable hydrogen spillover rate of formic acid (FA) with polyvinylpyrrolidine imine (PVPI) modifying its surface. The presence of PVPI boosts the catalytic selectivity and activity of CuPd NWN for FA dehydrogenation and, more importantly, serves as a modem to tune the HS rate of FA and to stoichiometrically hydrogenate NO3− and NO2− to N2 at room temperature. The density functional theory (DFT) reveals that the CuPd (130 h−1) has a weaker HS rate than AgPd (390 h−1), but the CuPd (> 99%) has a higher utilization of HS than AgPd (31%). Our studies demonstrate a new approach of tuning the FA HS rate and maximizing the application for stoichiometric chemoselective hydrogenation reaction, which will be important for hydrogen generation and its applications.

The research and development of novel protective structures with excellent mechanical load-bearing and energy-absorbing characteristics are one of the current interests in aerospace, marine, and au...

In this study, a cryogenic abrasive air jet machining (CAAJM) experimental system is designed and built based on the glass transition characteristics of polydimethylsiloxane (PDMS). Fixed processing parameters are then used to evaluate the effectiveness of machining PDMS by abrasive air jet machining (AAJM) at room and cryogenic temperatures, and the results show that cryogenic could improves the processing quality of PDMS. Furthermore, the potential effects of cryogenic treatment on the mechanical properties and wettability of PDMS were analyzed. The results showed that the mechanical properties was slightly decreased under cryogenic treatment, but the wettability was slightly increased. These resulted will further promote the application of CAAJM in the field of microfluidic analytical system. Based on this, experiments are conducted into how microchannel processing quality is influenced by the scanning speed and the erosion distance, pressure, and angle. The results show that better PDMS microchannels are processed when the erosion distance is 2.5–3.5 μm, the erosion pressure is 0.4 MPa, the erosion angle is 60–75°, and the scanning speed is 0.25 mm/s.

This brief presents a new quenching circuit with a metal fuse that aims to protect readout integrated circuit (ROIC) from breakdown due to unexpectedly high voltage from Geiger-mode avalanche photodiode (GmAPD) arrays. Fuse resistances in states of pre-burnout and post-burnout are investigated to satisfy requirements of rapid quenching and high voltage protection, respectively. Several fuse options using commercial mixed-signal CMOS processes, such as metal and polysilicon, are compared in detail. Meander metal fuse is the most suitable candidate according to measurement results. A rapidly quenching circuit integrated with metal fuse is developed using a 0.18 $\mu \text{m}$ CMOS process. After being bonding with GmAPDs and resistors, test results show that this circuit could endure a high voltage of 75 V, demonstrating that this innovative design can contribute in a low-cost and high-reliable way to high-yield large-format GmAPD arrays.

Purpose The purpose of this paper is to study the propagation of inhomogeneous waves in a partially saturated poro-thermoelastic media through the examples of the free surface of such media.. Design/methodology/approach The mathematical model evolved by Zhou et al. (2019) is solved through the Helmholtz decomposition theorem. The propagation velocities of bulk waves in partially saturated poro-thermoelastic media are derived by using the potential functions. The phase velocities and attenuation coefficients are expressed in terms of inhomogeneity angle. Reflection characteristics (phase shift, loci of vertical slowness, amplitude, energy) of elastic waves are investigated at the stress-free thermally insulated boundary of a considered medium. The boundary can be permeable or impermeable. The incident wave is portrayed with both attenuation and propagation directions (i.e. inhomogeneous wave). Numerical computations are executed by using MATLAB. Findings In this medium, the permanence of five inhomogeneous waves is found. Incidence of the inhomogeneous wave at the thermally insulated stress-free surface results in five reflected inhomogeneous waves in a partially saturated poro-thermoelastic media. The reflection coefficients and splitting of incident energy are obtained as a function of propagation direction, inhomogeneity angle, wave frequency and numerous thermophysical features of the partially saturated poro-thermoelastic media. The energy of distinct waves (incident wave, reflected waves) accompanying interference energies between distinct pairs of waves have been exhibited in the form of an energy matrix. Originality/value The sensitivity of propagation characteristics (velocity, attenuation, phase shift, loci of vertical slowness, energy) to numerous aspects of the physical model is analyzed graphically through a particular numerical example. The balance of energy is substantiated by virtue of the interaction energies at the thermally insulated stress-free surface (opened/sealed pores) of unsaturated poro-thermoelastic media through the bulk waves energy shares and interaction energy.

A numerical study was performed to investigate the combustion characteristics of hydrogenated catalytic biodiesel (HCB)/gasoline reactivity controlled compression ignition (RCCI) with dual-fuel direct injection at low load condition. The results indicated that compared with the conventional port injection RCCI, the dual-fuel direct injection can effectively control the distribution of in-cylinder gasoline mixture and improve the incomplete combustion phenomenon. The delay of start of injection (SOI) of gasoline can weaken stratified combustion, shorten combustion duration, reduce combustion efficiency, decrease NOx emission and increase soot emission. In contrast, the delay of SOI of HCB can intensify stratified combustion, prolong combustion duration, increase combustion efficiency, increase NOx emission and reduce soot emission. Compared with gasoline injection timing, HCB injection timing has a more profound effect on combustion efficiency and indicated thermal efficiency. When HCB injection timing was in the range of -25° ATDC (after top dead center) to -20° ATDC and gasoline injection timing of -50° ATDC to -45°ATDC, the engine has a better performance, with the combustion efficiency about 94 %, the indicated thermal efficiency around 45 %, and the NOx and soot emissions in the original exhaust less than the limit value of Euro VI standard.

The increase of base current is the main damage effect of p-n-p bipolar junction transistors (BJTs) subjected to ionization radiation. The Gummel–Poon (G-P) model is widely used to describe the electrical performance of BJTs. For the purpose of simulating the ionization damages on bipolar circuit performance, this article develops a G-P SPICE model that incorporates the latest formula of excess base current. Then, this article reports the ionization damage effects on a p-n-p controlled common-emitter amplifier circuit that is a key unit in the bipolar integrated circuit. After $\gamma $ -ray exposures, both the output voltage of the common-emitter circuit and its relaxation time decrease. Two novel phenomena are observed for the ionization damages on the common-emitter circuit, i.e., the degradation of output voltage exhibiting time-dependent effects and sublinear dependence on dose. Moreover, this article proposes, from perspectives of SPICE simulation and circuit theory, the mechanisms behind the characteristics of degradation from ionization damage in the common-emitter circuit. The SPICE simulations provide a good fit to the experimental data for the response of output voltage of a 2N2907 p-n-p controlled common-emitter circuit to ionization damage with a dose up to 2000 Gy(SiO2). Also, this article presents two applications of the new SPICE model in quantitatively describing the ionization damages on basic circuits, including crosstalk-related degradation and process-related statistical distribution of degradation.

Microwave-assisted ignition is a new ignition method, which has the advantages of reliable ignition and high ignition energy and requires no preheating. In this study, experimental methods were used to study the microwave-assisted ignition and combustion characteristics of ADN-based liquid propellant, and the effects of microwave power and propellant flow rate on combustion flame structure, spectral emission characteristics, and flame temperature were investigated. In the experiment, a microwave-assisted ignition experimental device was established first. The ADN-based liquid propellant was injected into the microwave high-energy region from the bottom of the resonator through a hollow straight tube with an inner diameter of 1 mm, and the gas was introduced in a coaxial manner. The research results demonstrated that when the microwave power increased from 1000 to 2000 W, the flame height increased from 11.12 to 17.32 mm; the free radical intensity of C2*, NH2, and HNO* increased significantly; the flame temperature increased by about 28.9%. The increase in microwave power is helpful to the generation of intermediate products and the combustion performance of propellant is better. When the propellant flow rate was increased from 25 to 45 mL/min, it was found that the spray combustion effect was the best when the propellant flow rate was 30 mL/min, the flame height increased by 25.2%, and the flame temperature increased by about 11.3%.

A conduction cooled high peak power, narrow linewidth, and sub-nanosecond multi-beam laser as an excellent candidate for non-scanning lidar is demonstrated. This laser is based on master oscillator power amplifier (MOPA) scheme which consists of a pulse pumped Nd:YAG/Cr4+:YAG microchip laser as the master oscillator and a high efficient grazing incidence Nd:YVO4 slab amplifier, and the output beam is expanded to 100 mm diameter by a 50× low aberration Galileo beam expander and then divided into a 50×2 staggered arrangement multi-beam array by a diffractive laser splitter. The laser operates at 1 064.28 nm with a spectral linewidth about 20 pm, which generates 1 mJ, 0.78 ns pulses at 7 kHz rate. The fluctuation of output power is less than ±2% when it works continuously for 1 h. The energy uniformity of the 100 sub-beams is up to 90%, the divergence of each sub-beam is about 20 µrad, and the total transmission efficiency of the diffractive laser splitter is more than 85%.

The use of cryogenic abrasive jet machining (CAJM) technology for polydimethylsiloxane (PDMS) materials is increasing rapidly due to its high material removal rate and high surface quality. However, how the material properties of PDMS affect the machining properties under cryogenic conditions is still an unsolved problem. Firstly, the thermodynamic and mechanical properties of PDMS materials are studied by dynamic thermo-mechanical analysis and universal material testing. The results show that the PDMS material’s embrittlement temperature is 126 K. Secondly, evaluation of cooling temperature of PDMS during CAJM shows that the machined area has reached embrittled state. Thirdly, the effect of PDMS material’s embrittlement on the machining behaviour is studied. The experimental results show that the PDMS material exhibit increased abrasive erosion at medium-angle under cryogenic conditions and shows a semi-brittle wear mechanism. Furthermore, the erode surface’s roughness is evaluated. The result shows that the roughness decreases with decreasing air pressure at the same impact angle; with increasing impact angle, the roughness shows a trend of increase initially and then decreases. This work shows that the PDMS material’s embrittlement and the erosion response behaviour during CAJM are due to the combined effects of thermo-mechanical properties and material removal mechanisms, providing a better understanding of CAJM technology.

A damping model of fiber reinforced composites was established in this study. Meanwhile, the accuracy of the damping model was verified through experiments. Subsequently, the factors affecting the damping ratio and dynamic response under sinusoidal excitation force of fiber reinforced composites were explored and the measures improving the damping ratio were proposed. The damping model of the fiber reinforced composite was applied to its dynamic equation, and then the dynamic response curves were calculated by the direct time integration method, and the calculated dynamic response curves were compared with the experimental dynamic response curves. The two groups of curves almost coincided, verifying the excellent accuracy of the damping model. Additionally, this study discussed the effects of the fiber volume fraction, the thickness of each layer, the number of layers, the orientation of laying-up, and the sequence of layers on the damping ratio and dynamic response of composite material laminates. The damping model proposed in this paper was suitable for calculating the response curves of composite laminates under sinusoidal concentrated loads. The damping model can be used to calculate the response of the laminate in the elastic range. The accuracy of the model was verified through experiments in the frequency range of 10–200 Hz. The method of calculating the dynamic response of fiber reinforced composites proposed in this study can be easily inserted into the finite element analysis software and directly applied to engineering practice.

Lead halide perovskite solar cells (PSCs) have been rapidly developed in the past decade. Owing to its excellent power conversion efficiency with robust and low-cost fabrication, perovskite quickly becomes one of the most promising candidates for the next-generation photovoltaic technology. With the development of PSCs, the interface engineering has witnessed its increasingly critical role in maximizing the device performance as well as the long-term stability, because the interfaces in PSCs are closely correlated with the defect management, carrier dynamics and surface passivation. This review focuses on interfacial modification between the perovskite active layer and the charge transport layer, as well as the recent advances on high-efficiency and stable PSCs driven by interface engineering strategies. The contributing roles of interface engineering in terms of defect passivation, inhibiting ion migration, optimization of energy band alignment and morphological control are discussed. Finally, based on the latest progress and advances, strategies and opportunities for the future research on interface engineering for PSCs are proposed to promote the development of perovskite photovoltaic technology.

A homogeneous α-cellulose film was prepared by regeneration method from ZnCl2/CaCl2/cellulose mixed system and was further combined with sodium lignosulfonate (SLS) by crosslinking through interaction hydrogen bonds and “bridge linkages”. The physicochemical and antibacterial performance of films were all investigated and results showed that modified films exhibited stronger tensile strength, higher thermal stability, lower hydrophilic effect, better UV shielding as compared with those of pure cellulose film, and especially, better antibacterial ability derived from the presence of phenolic and sulfonate groups in SLS. This study proposed a simple and sustainable method for fabricating a multifunctional and environmentally friendly composite film by using two main lignocellulose resources as raw materials.

Transition metal alloy electrocatalysts have sparked intense interest for their use in oxygen reduction reaction (ORR). However, there is almost no corresponding research on the alloy active sites. In this study, CoNi alloy nanoparticles embedded in bamboo-like N-doped carbon nanotubes (CoNi-NCTs) as catalysts constructed by a facile pyrolysis of Prussian blue analogs were investigated. The density functional theory calculation reveals that the oxygen molecules are more easily adsorbed on the Ni sites in these catalysts, while the Co sites favor the formation of OOH⋆ intermediates during ORR. In addition, the cooperation of the CoNi alloys with the N-doped carbon benefits electron transfer and promotes electrocatalytic activity. The optimized CoNi-NCT shows remarkable ORR catalytic activity with an half-wave potential (E1/2) of 0.83 V, an onset potential (Eonset) of 0.97 V, and superior durability, all of which surpass the commercial Pt/C catalysts. The assembled zinc-air battery delivers a small charge/discharge voltage gap of 0.86 V at 10 mA cm−2, a high-power density of 167 mW cm−2, and good stability (running stably over 900 cycles).

Methylene blue, a prevalent cationic type dye, has been extensively utilized in textile industry. Lignin generates as a byproduct and its utilization is required to add a potential economic benefit of a biorefinery process. Lignin-derived porous biochar, as a promising adsorbent, was propitiously prepared by chemical modification with different oxidation number manganese compounds (KMnO4, MnSO4, and MnO2). The adsorption capacity of MnO2-loaded biochar to methylene blue dye was substantially higher relative to original biochar. The maximum adsorption capacity was 248.96 mg/g and removal rate was 99.73%, as compared to 234.65 mg/g and 94.0% for unmodified biochar. In comparison, the decolorization rate of the modified biochar exceeded 95%. Substantial results showed that methylene blue has a strong binding affinity with MnO2 modified biochar. Adsorption kinetics was described by a quasi-second order model and methylene blue adsorption isotherm was better fitted by Langmuir model. The research provides a promising way for the removal of methylene blue from wastewater through the manufacture of adsorbent from byproduct of biorefinery process.

The spin Hamiltonian parameters (SHPs, g factors and hyperfine structure constants) defect structure for LiMgPO4 doped with 0.1% Co2+ at 4.2 K are theoretically investigated from the perturbation formulas of the SHPs for a rhombically distorted octahedral 3d7 cluster. The impurity Co2+ on host Mg2+ site is found to suffer the larger axial relative compression ratio ρ (≈ 0.76%) and the planar angular variation Δφ (≈ 6.64°) related to the host oxygen octahedron due to size mismatch. The calculated SHPs based on the above defect structure show good agreement with the measured results. Present study can be helpful to the preparation and characterization for the local structures for transition-metal impurities in lithium-magnesium phosphate, which may is helpful to search for the phosphor materials with better dosimetric characteristics.

Experiments to characterize the constant-rate gas depleted production behavior in core samples were performed to study the areal gas flowing mechanism of a high-pressure low-permeability heterogeneous gas reservoir, including a newly designed long-core experiment on areal heterogeneity constant-rate gas depleted production considering fracturing. In the experiments, the fluid pressure increased up to 45 MPa, and the cores of the near-wellbore high permeability area before and after fracturing and the cores of the low permeability non fractured area were connected in series to simulate the gas flowing process of the dual-area composite gas reservoir. When the irreducible water saturation is considered, the gas permeability in a high permeability area cater fracturing increased threefold. Experimental results indicated that the pressure difference in the near-wellbore high permeability area decreased rapidly after fracturing and increased in the low permeability area. The recovery:factor of each area increased titter fracturing. Fracturing could have a significant effect on increasing the recovery factor when the average permeability is relatively low. The greater the gas rate, the higher is the built-up pressure alter shut-in. Fracturing in the near-wellbore area may cause a significant decrease in the shut-in built-up pressure value.

The polymer polydimethylsiloxane (PDMS) is used widely in microfluidic chips. At room temperature, when PDMS is machined by micro-abrasive jet machining (MAJM), its high elasticity means that it often suffers from processing defects such as abrasive embedding and a surface deterioration layer. Cryogenic micro-abrasive jet machining (CMAJM) based on the glass transition has been proposed, but a model for predicting the volume of material removed is yet to be established. In this study, orthogonal experiments are used to investigate how different processing parameters influence the material removal volume. The results show that the material removal volume is largest when the jet pressure is 0.6 MPa, the erosion angle is 60°, the erosion distance is 3.5 mm, and the scanning speed is 0.2 mm/s. A model is established to predict the material removal volume during the CMAJM of PDMS, and single-factor experiments are used to assess the model qualitatively. The results show that the model offers good predictions of how the material removal volume changes with the scanning speed and jet pressure.

Precise control of the composition and structure of active sites in an atom-by-atom fashion remains insuperable for heterogeneous catalysts. Here, we introduce tailor-made catalytic sites for the cycloaddition of CO2 to epoxides achieved by implementing Ag atoms at different levels of liberation in atomically precise Au nanoclusters. Our results reveal that a single open Ag site on the Au19 Ag4 cluster improves the ring-opening of epoxides and sequent CO2 insertion, while the partially exposed Ag site on the Au20 Ag1 cluster exhibits a weak affinity for epoxides and poor efficiency for CO2 capture. Structural tunability imparted by the atom-by-atom tailoring and unusual atomic charges distributed on Au and Ag atoms of the three clusters seem to be crucial for promoting challenging bond cleavages and formations in the chemical utilization of CO2 .

The heat transfer performance of showerhead film cooling on the vane leading edge was numerically investigated considering representative lean burn combustor swirling outflow. Three cases with different inflow conditions (uniform inflow, positive swirling inflow, and negative swirling inflow) and three cases with different film injection angles (45°, 90°, and 135°) were studied. As the first study to explore the showerhead film design principle under swirling inflow, a newly designed asymmetrical counter-inclined (45° and 135°) film cooling was also proposed. To examine the design principles, the cooling effectiveness, heat transfer augmentation, and heat flux reduction of the newly designed asymmetrical case were evaluated compared with the traditional symmetrical case. The results show that the swirling inflow introduces obvious radial pressure gradient on the vane. The radial pressure gradient is the key influence factor to deflect the coolant migration, decrease the cooling effect, and degrade the homogeneity. The film with opposite orientation to the radial pressure gradient can weaken the deflect effect. The radial pressure gradient direction differs in different regions, making it impossible for the film with congruent injection orientation to simultaneously resist the pressure gradient on the entire vane. For the new design, the boundary line of the counter-inclined holes is consistent with the twisted stagnation line to guarantee that the injection orientation of all the film holes is opposite to the radial pressure gradient. As expected, the new design can effectively weaken the deflection effect and show uniform film distribution. The higher coolant mass ratio provides more obvious enhancement effect. At coolant mass ratio 3.71% and 4.56%, the overall area-averaged heat flux reduction (Δ q) is increased by 0.311 and 0.576, and the overall area-averaged relative standard deviation is reduced by 12.17 and 11.66 compared with the traditional design. The results have confirmed the adaptability of the film design principle under swirling inflow.

Bifunctional electrocatalysts with high activity toward both oxygen reduction and evolution reaction are highly desirable for rechargeable Zn-air batteries. Herein, a kind of carbon nanotube (CNT) supported single-site Fe-N-C catalyst was fabricated via pyrolyzing in-situ grown Fe-containing zeolitic imidazolate frameworks on CNTs. CNTs not only serve as the physical supports of the Fe-N-C active sites but also provide a conductive network to facilitate the fast electron and ion transfer. The as-synthesized catalysts exhibit a half-wave potential of 0.865 V for oxygen reduction reaction and a low overpotential of 0.442 V at 10 mA·cm−2 for oxygen evolution, which is 310 mV smaller than that of Fe-N-C without CNTs. The rechargeable Zn-air batteries fabricated with such hybrid catalysts display a high peak power density of 182 mW·cm−2 and an excellent cycling stability of over 1,000 h at 10 mA·cm−2, which outperforms commercial Pt-C and most of the reported catalysts. This facile strategy of combining single-site Metal-N-C with CNTs network is effective for preparing highly active bifunctional electrocatalysts.

The natural gas (NG) jet characteristics of NG/diesel dual-fuel injection under different NG injection pressures and dual-fuel injection intervals were studied in a constant volume chamber. The schlieren images showed that the development of NG jet was restricted in both axial and radial directions by diesel spray under dual-fuel injection conditions. Consistently, dual-fuel injection reduced NG jet tip penetration, NG jet cone angle and NG jet volume, yet increased average fuel-air equivalent ratio, compared to NG single-fuel injection. The increase of NG injection pressure from 3 MPa to 5 MPa enhanced NG jet tip penetration and NG jet volume, yet decreased jet cone angle under both single-fuel and dual-fuel injection conditions. The negative effects of diesel spray on NG jet became gradually reduced with the increase of injection interval. When the injection interval was longer than 1.5 ms, NG jet characteristics were close to those under single-fuel conditions.

A binder is an important component in lithium-ion batteries and plays a significant role in maintaining the properties of active substances. Most studies in the field of binders have only focussed on physical properties such as bonding performance. Here, a polyacrylic acid-modified binder was designed and adapted to Li[Ni0.8Co0.1Mn0.1]O2, which enhanced the electrochemical stability of Li[Ni0.8Co0.1Mn0.1]O2 from 30.2 to 66.6% (300 cycles at 1 C). We for the first time discovered that this was caused by a chemical reaction between polyacrylic acid and the residual lithium on the surface during the cycling, which formed a lithium propionic acid coating layer and maintained the stability of the layered structure.

During the hot strip tandem rolling (HSTR) process, the strip is compressed and elongated continuously, causing significant elastic deformation of rolls. At the same time, the strip temperature undergoes rapid increase and decrease, and distributes unevenly along the strip width direction. Elastic deformation of rolls and strip temperature variations have a significant effect on strip deformation, resulting in various strip shape. In this study, a novel three-dimensional (3D) coupled thermal-mechanical elastic-plastic finite element (FE) model for the HSTR is proposed based on the segmentation modeling strategy, where the finish mill is divided into several sub-models. The data transfer technology is developed to integrate the sub-models into a whole model via transferring the strip crown and temperature among the sub-models. Furthermore, the active and deactive element method, rigid pushing technology, and element remesh are also used to improve the calculation efficiency and accuracy of the model. Multi-objective parameters, such as strip temperature, strip crown, elastic deformation of roll stacks, and rolling force during the HSTR process are studied systematically using the developed FE model. The results show that the calculated strip temperature and strip crown after F7 agree well with the measured values, and the relative error between calculated and measured rolling force at each stand is less than 10%. This work offers a fresh perspective on the HSTR simulation.

Natural magnetite formed by the isomorphism substitutions of transition metals, including Fe, Ti, Co, etc., was activated by mechanical grinding followed by H2 reduction. The temperature-programmed reduction of hydrogen (H2-TPR) and temperature-programmed surface reaction of carbon dioxide (CO2-TPSR) were carried out to investigate the processes of oxygen loss and CO2 reduction. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS). The results showed that the stability of spinel phases and oxygen-deficient degree significantly increased after natural magnetite was mechanically milled and reduced in H2 atmosphere. Meanwhile, the activity and selectivity of CO2 reduction into carbon were enhanced. The deposited carbon on the activated natural magnetite was confirmed as amorphous. The amount of carbon after CO2 reduction at 300°C for 90 min over the activated natural magnetite was 2.87wt% higher than that over the natural magnetite.

Carboxymethyl chitosan (CMCS)-based hydrogels have antibacterial activity, and have shown the abilities of preventing wound infection, promoting cell proliferation, accelerating collagen deposition, and stimulating hyaluronic acid formation during wound healing. As a hormone produced by the pineal gland in humans and animals, melatonin promotes skin wound healing by regulating the release of inflammatory mediators and accelerating the proliferation and migration of cells, angiogenesis, and collagen deposition. However, the combined effects of CMCS and melatonin on wound healing remain unclear. Injectable CMCS-based hydrogels containing melatonin were prepared, and their healing effects were evaluated using a full-thickness cutaneous wound model in rats. Compared with the control and the hydrogel with no melatonin groups, the melatonin-loaded hydrogel significantly increased the percentage of wound closure, promoted the proliferation of granulation tissue and re-epithelialization, and accelerated collagen deposition. Additionally, the melatonin-loaded hydrogel promoted angiogenesis and vascular endothelial growth factor receptor protein expression and increased the expression of cyclooxygenase-2 and inducible nitric oxide synthase. The melatonin-loaded hydrogel also markedly increased the expression of collagen III, α-smooth muscle actin, and transforming growth factor-β1 proteins and reduced collagen I expression. These results suggest that the melatonin-loaded hydrogel promoted granulation tissue formation and accelerated wound healing by reducing inflammation and promoting angiogenesis and collagen deposition.

This paper presents model tests (macro aspect) and microstructure tests (micro aspect) for investigating the consolidation behavior of Tianjin dredged clay using the prefabricated vertical drain air-booster vacuum preloading (PAVP) and tube air-booster vacuum preloading (TAVP) methods. The mechanism of air-booster vacuum preloading (AVP) using a spring-like system is explained. The main difference between these two methods is the air-boosting equipment. A new anticlogging air-booster prefabricated vertical drain (PVD) is used in the PAVP technique and a self-designed air-booster tube is used in the TAVP technique. In the model tests, a comparison of the variables that are monitored during reinforcement (vacuum pressure, surface settlement, water discharge, and pore-water pressure) and after reinforcement (water content, dry density, and vane shear strength) is conducted. The results indicate that the consolidation behavior of Tianjin dredged clay using the PAVP method is better than that using the TAVP method. PAVP more efficiently mitigates the issue of water-draining PVD clogging and significantly accelerates drainage consolidation. In addition, in the microstructure tests, a comparison of the variables that are monitored after reinforcement (via scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP)) is conducted, and the results further explain the model test results.

SUMMARYThe seismic reflection/transmission (R/T) problems have been investigated for various complicated porous materials described by various poro-viscoelastic theories. However, it was also reported that even for a simple plane wave at a plane interface between two dissimilar isotropic viscoelastic solids, they were proved to be more complicated than expected and still required further study. The main difficulty is to correctly select the signs of the vertical components of the slowness vectors (or vertical slowness q) of the viscoelastic R/T waves to calculate R/T coefficients (including the relevant displacement amplitudes and phase delays) without unphysical discontinuity but with elastic consistence. Logically, if this problem had not been solved in the relatively simple case of waves in isotropic viscoelastic materials, it would not be expected to be solved in the complicate porous media. The existing criterion to select the sign of vertical slowness for poro-viscoelastic waves is the radiation condition that has been reported to cause unphysical discontinuity for the R/T coefficients of viscoelastic waves. In this paper, the radiation condition is illustrated to cause the unphysical discontinuities. Meanwhile, the continuity criterion is for the first time applied in the R/T coefficients calculation for poro-viscoelastic waves. The continuity criterion is simply suggested to be conducted in the complex vertical slowness square (q2) plane by swapping the sign of the q for the relevant wave whose q2 locus crosses the branch cut. Furthermore, the elastic consistence is also for the first time considered for poro-viscoelastic waves. We stress the importance of consistence between the R/T coefficient equations of poro-viscoelastic waves and those of pure elastic waves, which includes three consistent assumptions: time dependence of harmonic waves, the z-direction of the coordinate system and particle motion (polarization) vectors. With the numerical examples of poro-viscoelastic interfaces, the R/T coefficients of three types of incident waves, that is, homogeneous S waves, inhomogeneous S waves and homogeneous P waves, are investigated for frequencies 1000 and 0.001 Hz, representing highly and weakly dissipative poro-elastic waves, respectively. The calculated R/T coefficients are shown to be continuous without unphysical discontinuity under the continuity criterion. For the cases of homogeneous S- or P-wave incidence, the R/T coefficients of poro-viscoelastic waves with 0.001 Hz well match the corresponding coefficients of elastic waves in terms of amplitudes and phases, and thus the elastic consistence is well confirmed. For the highly dissipative poro-elastic waves (1000 Hz), the R/T coefficients significantly depend on the degrees of inhomogeneity of the incident waves. In a similar manner to the viscoelastic wave, a higher degree of inhomogeneity of an incident wave better tends to smooth the R/T coefficients of poro-viscoelastic waves. The methods suggested in this paper to solve the problems of R/T coefficient continuity and elastic consistence for the poro-viscoelastic waves can also be applied for viscoelastic waves as the special case.

Electrical conductivity and interfacial polarization are two crucial factors that affect the electromagnetic absorption (EMA) performance of dielectric semiconductors. In this work, we report an efficient surficial-coating strategy to tune the interfacial polarization and dielectric properties of molybdenum disulfide (MoS2) nanosheets. In this strategy, undoped and N-doped carbon films have been successfully coated on MoS2 nanosheets through a hydrothermal deposition and pyrolysis process. The EMA performance of MoS2 nanosheets was improved remarkably after carbon coating. It is found that the maximal absorption reaches −56.97 dB at 5 GHz while the effective absorption bandwidth (below −10 dB) reaches 5.44 GHz. A model referring to elevated electrical conductivity and improved interfacial polarization was used to explain the mechanism of enhanced EMA performance. This research greatly supports the development of novel MoS2 based high-performance EMA materials.

A DEM-embedded-finite-element-method (DEFEM) with a 2D-asymmetric circular particle heat conduction model is proposed. DEFEM combines the discrete-element (DE) and finite-element model (FEM) with heat conduction. With embedded discrete elements (EDE), DEFEM solves heat conduction between particles and temperature field inside particles. EDE solves heat conduction in asymmetric circular element, and FEM simulates transient heat conduction after the heat flux at boundaries is known. Verified by experiments, results show that DEFEM can accurately simulate transient heat conduction of pebble beds. Discrete-model (DM) and continuum-model (CM) are comparatively analyzed under the same thermal responses and temperature distributions. In CM, the standard function of thermal conductivity is fitted with an attenuation part, an increment part and a constant part. The constant part is defined as effective thermal conductivity (ETC) of CM, which is directly proportional to that of DM, and independent of heat capacity. Herein, ETC of the CM is a key parameter, which could be used to measure the overall heat transfer capability of the bed

Single-atom catalysts (SACs) often exhibit superb catalytic activity due to their high atom utilization. By comparing the adsorption energies of O2 and CO adsorbed on TM@C9N4, we expect that Co and Ni anchored at the cavity of C9N4 exhibit a higher catalytic activity for CO oxidation. For the entire reaction, the Eley-Rideal, New Eley-Rideal, Ter-molecular Eley-Rideal and Langmuir-Hinshelwood mechanisms are all taken into account. Depending on the reaction mechanisms, the catalysts Co@C9N4 and Ni@C9N4 show excellent activity, with a kinetic energy barrier ranging from 0.19 eV to 0.54 eV for the former, while the corresponding energy barrier is 0.26 eV to 0.44 eV for the latter. The superior stability and activity of Co/Ni@C9N4 can efficiently oxidize the large amounts of CO caused by inadequate combustion of coal and natural gas resources.

With atomically precise gold nanoclusters acting as a starting unit, substituting one or more gold atoms of the nanocluster with other metals has become an effective strategy to create metal synergy for improving catalytic performances and other properties. However, so far detailed insight into how to design the gold-based nanoclusters to optimize the synergy is still lacking, as atomic-level exchange between the surface-gold (or core-gold) and the incoming heteroatoms is quite challenging without changing other parts. Here we report a Cd-driven reconstruction of Au44(DMBT)28 (DMBT = 3,5-dimethylbenzenethiol), in which four Au2(DMBT)3 staples are precisely replaced by two Au5Cd2(DMBT)12 staples to form Au38Cd4(DMBT)30 with the face-centered cubic inner core retained. With the dual modifications of the surface and electronic structure, the Au38Cd4(DMBT)30 nanocluster exhibits distinct excitonic behaviors and superior photocatalytic performances compared to the parent Au44(DMBT)28 nanocluster., With dual modifications of the surface and electronic structure, Au38Cd4(DMBT)30 exhibits distinct excitonic behaviors and photocatalytic performances compared to Au44(DMBT)28.

The selective late-stage functionalization of BN-containing polycyclic aromatic hydrocarbons (BN-PAHs) is very challenging. Herein, dithienoazaborines (BNDT, 3a and 3b) were synthesized as model compounds, and two kinds of selective functionalized BNDT precursors, 4a and 4b were synthesized due to the strong polar effect of the BN bond, leading to a series of BNDT derivatives for the following coupling reactions. Based on this, two kinds of BNDT-based small molecules and oligomers with BN bonds on the conjugated main chain and side chain were synthesized accordingly. The BNDT derivatives (5b/6b/7b) with a BN bond on the conjugated side chain showed lower LUMO energy levels and narrower band gaps than those with a BN bond on the conjugated main chain (5a/6a/7a). Different modifications and polymerization have effects on the photophysical properties and all derivatives are highly selective to fluoride ions. This work realized a new strategy for selective late-stage functionalization of BN-PAHs with selective π-conjugated extension, laying a solid foundation for the subsequent BN chemistry and application of functionalized BN-PAHs.